How to get my 13 year old son to socialize

I have a super great 13 year old son. He is high honors in school. Is very interested in cooking and gardening and all outdoor activities. As long as he can do those things by himself. The only activity we can get him to do with kids his age is spring soccer for 2 months. I ask him all the time to try to make new friends and he keeps telling me he is fine. I don't want him to miss out on the fun you can have with friends. What do I do??